Spray gun

ABSTRACT

A spraying apparatus for spraying liquid surface treatment material which includes a gas inlet, a liquid inlet and an outlet nozzle. The apparatus also has a needle valve for regulating the supply of surface treatment material to the nozzle. The needle valve is at least partially located within a gas outlet chamber and is adapted so as to cause minimal disruption to the gas flow from the gas inlet to the nozzle. To further aid gas flow efficiency, the gas supply passage is substantially straight, the outlet chamber has a laterally outwardly tapering inlet and an inwardly tapering outlet and a smooth radius of curvature from the gas supply passage into the outlet chamber. There is also provided a control means for controlling the axial movement of the needle valve, the control means being provided with indicator means so as to provide an accurate, repeatable control means

The present invention relates to an apparatus to improve efficiency inthe spraying of materials. Particularly, but not exclusively, theinvention is a spray gun for the application of paint and similarmaterial surface treatments, particularly water-based paints.

Various known spray guns have been developed for the purpose of reducingpressure losses between the air inlet and air outlet of guns.Conventional spray guns, high volume-low pressure (HVLP) guns and lowvolume-low pressure (LVLP) guns all suffer from a reduction in airpressure through the gun. In some instances, this reduction can be over80%.

HVLP guns require very large volumes of air to maintain an acceptableatomization of the spray material. For example, to pass large volumes ofair through an HVLP gun requires very high pressures to maintain a 10psi (0.69 bar) pressure in the head of the gun, resulting in an averageair consumption rate of approximately 20 scfm (566 1/min). With an inputpressure of 75 psi (5.1 bar), the air expands on leaving the gun toregain its pre-compression volume. This will result in the atomizedspray material being taken in all directions by the expanding air, inspite of the exit pressure being only 10 psi (0.69 bar). Thus, the sprayoutput of HVLP guns can prove difficult to control.

Despite having a smaller clearance between the fluid tip and air capthan in HVLP guns, LVLP guns also suffer from pressure loss within thegun body. As a result, LVLP guns still require a high inlet pressure of50-60 psi (3.45-4.14 bar) to operate at an atomizing (outlet) pressureof 15-18 psi (1.03-1.24 bar). Air consumption rates of LVLP guns rangefrom 14-18 scfm (396-510 l/min), thus illustrating that LVLP guns arealmost as inefficient as HVLP guns.

The main cause of the aforementioned inefficiency of HVLP and LVLP gunsis the arrangement of the air passages within the gun body. The designand layout of air passages in the known guns leads to poor internal airflow efficiency.

It is therefore the aim of the present invention to provide a sprayingapparatus which has a significantly improved air flow efficiency overknown spray guns.

According to a first aspect of the present invention, there is providedan apparatus for spraying liquid surface treatment material, theapparatus comprising:

-   -   a liquid inlet for supply of the liquid surface treatment        material;    -   a gas inlet for supply of pressurized gas to be mixed with the        liquid surface treatment material;    -   an outlet nozzle through which the gas and liquid surface        treatment is sprayed;    -   a control needle valve arranged for axial movement on a first        axis and adapted to regulate the supply of the liquid surface        treatment material to the outlet nozzle;    -   a gas valve operable between an open position and a closed        position;    -   a gas chamber communicating with said outlet nozzle and arranged        to co-axially surround the control needle valve; and    -   a gas supply passageway having first and second portions with        first and second diameters, respectively, the first portion        connecting said gas inlet and said gas valve and the second        portion connecting said gas valve and said gas chamber;    -   wherein the first and second portions of the gas supply        passageway are coaxial and the first and second diameters are        substantially equal such that the gas supply passageway has        substantially the same diameter over its entire length.

Preferably, the gas chamber has a first end portion adjacent the gassupply passageway, the first end portion having a radius of curvature soas to provide gas to the nozzle in a direction substantially parallel tosaid first axis, and wherein said apparatus is adapted to provide asmooth flow path for the gas therethrough. The radius of curvature issuch that the minimum radius of the internal surface of the first endportion of the gas chamber is 1.3 times the diameter of the gas supplypassageway.

Preferably, the gas chamber has an inner surface which tapers laterallyoutwardly from the first end portion of the gas chamber, the taperrunning in the direction of said outlet nozzle.

Preferably, the gas chamber includes a second end portion adjacent saidoutlet nozzle, the inner surface of said second end portion inwardlytapering towards said nozzle to provide a smooth flow path for gasflowing from the outlet chamber to the nozzle.

Preferably, said gas valve is located within said gas supply passageway.Preferably, said gas valve is an axially-sliding piston valve having anaperture therein whose diameter is substantially equal to the diameterof the gas supply passageway.

Preferably, said apparatus further comprises a trigger means adapted tooperate both said control valve and said gas valve.

Preferably, said control needle valve is partially located within saidgas chamber and includes a fluid tube having a fluid tube diameter and afluid tip having a fluid tip diameter substantially equal to or lessthan the fluid tube diameter. Preferably, said fluid tube has a taperedthroat portion located in said gas chamber, the throat portion having athroat portion diameter which is less than the fluid tube diameter.

According to a second aspect of the present invention, there is providedan apparatus for spraying liquid surface treatment material, theapparatus comprising:

-   -   a housing;    -   a liquid inlet for supply of the liquid surface treatment        material;    -   a gas inlet for supply of pressurized gas to be mixed with the        liquid surface treatment material;    -   an outlet nozzle through which the gas and liquid surface        treatment is sprayed;    -   a control needle valve adapted to regulate the supply of the        liquid surface treatment material to the outlet nozzle;    -   a gas supply passageway connecting said gas inlet to said outlet        nozzle; and    -   a control means for controlling the control needle valve, the        control means comprising a cap member received on said housing        and engaged with said control needle valve, the cap member being        adapted so as to be adjustable in the axial direction relative        to the housing to limit axial movement of the control needle        valve.

Preferably, said cap member and housing are provided with calibrationswhich indicate the amount of axial adjustment of the needle valve.

Preferably, the apparatus further comprises a gas valve operable betweenan open position and a closed position.

In a preferred embodiment, the gas valve is located in the gas supplypassageway and the apparatus further comprises a trigger means adaptedto operate both said control needle valve and gas valve.

In an alternative preferred embodiment, said control needle valve andgas valve are remotely operated. Most preferably, the control needlevalve is remotely operated by way of pressurised gas and the apparatusfurther comprises a piston chamber and a piston located in the pistonchamber, the piston adapted to engage said needle control valve whenactuated by said pressurised gas. The apparatus also comprises a boreconnecting the gas supply passageway and the piston chamber, such thatpressurised gas may pass through the bore to the piston chamber when thegas valve is in the open position.

Embodiments of the present invention will now be described, by way ofexample only, with reference to the accompanying drawings, in which:

FIG. 1 shows a side elevation view of a first embodiment of a sprayapparatus;

FIG. 2 shows a longitudinal cross-section of the first embodiment of thespray apparatus shown in FIG. 1;

FIG. 3 shows a longitudinal cross-section of a second embodiment of thespray apparatus;

FIG. 4 shows a longitudinal cross-section of a third embodiment of thespray apparatus;

FIGS. 5(a) and 5(b) show plan and side elevation views, respectively, ofa fourth embodiment of the spray apparatus;

FIG. 6 shows a cross-section through the fourth embodiment of the sprayapparatus, taken along line VI-VI of FIG. 5(a);

FIG. 7 shows a cross-section through the fourth embodiment of the sprayapparatus, taken along line VII-VII of FIG. 5(b);

FIG. 8(a) shows a side elevation of a fifth embodiment of the sprayapparatus; and

FIG. 8(b) shows a longitudinal cross-section through the fifthembodiment shown in FIG. 8(a).

Referring initially to FIG. 1, there is shown a first embodiment of aspraying apparatus, or spray gun, generally designated 10. The spray gun10 includes a housing 11 having a fluid control sleeve 12 slidinglyattached thereto, an air cap 13 which is held on the housing 11 by anair cap ring 13a threadedly received on the housing 11, and a regulatingvalve 14 for controlling the spray pattern of the gun. Also included onthe housing 11 is a needle valve cap, or fluid control nut, 15 which isattached to an internal needle valve arrangement and is threadedlyreceived on the control sleeve 12 to limit longitudinal adjustment ofthe needle valve. The needle valve cap 15 is provided with horizontalmarkings 16 spaced equidistantly about the circumference thereof which,in combination with vertical markings on the housing 11, allow theoperator to limit the movement of the needle valve and thus the amountof spray material passing through the nozzle. The housing has ahorizontal indicator line 17 a from which extend a plurality of verticalindicator lines 17 b at 1 mm intervals. By adjustment of the cap 15, theleading edge of the cap 15 can be adjusted to line up with any of thevertical indicator lines 17 b on the housing. In this embodiment, thereare ten horizontal markings 16 on the cap 15 at equidistant intervals.Adjustment of the cap 15 can be made such that one of the horizontalmarkings 16 of the cap 15 can line up with the horizontal indicator line17 a of the housing. Thus, if one horizontal marking 16 of the cap isaligned with the horizontal line 17 a of the housing, a 36 degreerotation of the cap will line up the subsequent horizontal marking ofthe cap 15. This procedure will be explained in more detail below.

The embodiment shown in FIG. 1 is a manual spray gun having a handle orgrip portion 19. The gun 10 has a trigger 18 that operates a gas controlvalve (not shown in FIG. 1) and also acts upon the fluid control sleeve12, such that fluid and gas are introduced to the gun simultaneously.

The operation of the first embodiment of the spray gun 10 will now bedescribed with reference to FIG. 2. Gas is provided to the gun 10 by wayof a gas inlet 20 and is then passed through a straight communicatingpassageway 21 to the gas control valve 23 and on to a gas chamber 26.The communicating passageway 21 has a first portion which connects thegas inlet 20 and the gas control valve 23, and a second portion whichconnects the gas control valve 23 to the gas chamber 26. Both portionsof the passageway 21 are arranged co-axially such that the entirepassageway is substantially straight. In addition, the diameters of thefirst and second portions are substantially the same such that there isno narrowing or widening of the passageway until it meets the gaschamber 26.

The gas control valve 23 is positioned perpendicular to the gas flow andcomprises an axially-sliding piston 24 which is acted upon by thetrigger 18. The piston 24 is provided with a bore 25 drilled through thepiston 24 perpendicular to the longitudinal axis of the piston 24. Thebore 25 is the same size as the bore of the communicating passageway 21,so that when the trigger 18 is depressed, the bore 25 aligns with thepassageway 21 to provide a smooth passage for the gas through the gascontrol valve 23 without creating turbulence.

Once through the gas control valve 23 and the second portion of thepassageway 21, the gas reaches the gas chamber 26. The gas chamber 26has a first end portion 29 adjacent the gas passageway 21 which has aradius of curvature sufficient to direct the gas flow into asubstantially horizontal direction when viewed in the accompanyingfigures. Preferably, the inside curve 36 of the first end portion 29 hasa radius of curvature which is at least 1.3 times the diameter of thepassageway 21.

As will be described below, the chamber 26 is also laterally tapered toaid gas flow therethrough. At a second end portion of the chamber 26which is remote from the first end portion 29 is an outlet nozzle 30through which the combined gas and spray material will exit the gun. Thesecond end portion of the chamber 26 has an inner surface 31 which has aradius of curvature which allows the inner surface 31 to taper inwardlyto the point where it reaches the output nozzle 30.

Partially located within the output chamber 26 is a control needlevalve, generally designated 40. The control needle valve 40 comprises afluid needle 43, fluid tube 44 and fluid tip 45. The cap 15 is providedwith a needle housing 41 in which the fluid needle 43 is housed. Thefluid needle 43 is biased by a needle spring 46 in a closed position.The needle housing 41 enters into a return spring piston 42 fitted tothe control sleeve 12 by a retaining means such as a circlip, forexample. A return spring 47 is also provided to bias the fluid sleeve 12and trigger 18 in the closed position.

The fluid needle 43 extends forward through the fluid tube 44 to rest ina seat of the fluid tip 45. The needle spring 46 biases the fluid needle43 such that it sits in the seat at the fluid tip 45, thereby blockingthe exit of fluid from the fluid tube 44 to the output nozzle 30. Thediameter of the fluid tip 45 is sized so as to be no greater than thediameter of the fluid tube 44, to prevent disruption to the gas flowthrough the output chamber 26 to the nozzle 30. Furthermore, theembodiment of FIG. 2 shows the use of a fluid tube 44 which has anarrower throat portion 44 a within the output chamber 26. The throatportion 44 a has a diameter less than that of the remainder of the fluidtube 44 and can be provided so as to provide a smoother passage for thegas as passes through the gas chamber 26.

In operation, the trigger 18 may always move the control sleeve 12 itsfull stroke. However, the cap 15 can be rotationally adjusted on thesleeve 12 to restrict or increase the intrusion of the needle housing 41into the return spring piston 42. In this way, the movement of the fluidneedle 43 can be adjusted relative to the full stroke of the sleeve 12.Where the cap 15 has been adjusted to restrict movement of the fluidneedle 43 entirely, a gap exists between the end of the needle housing41 and the end of the fluid needle 43 which is equal to the full strokeof the control sleeve 12. Thus, the trigger 18 can be operated and movethe sleeve 12 to its full stroke without moving the fluid needle 43 awayfrom its seat in the fluid tip 45.

As previously described with reference to FIG. 1, the gun housing has aplurality of vertical indicator lines 17 b along a portion of its lengthat 1 mm intervals. The cap 15 can be adjusted such that the leading edgeof the cap member 15 is aligned with one of the vertical indicator lines17 b. Once aligned, the horizontal markings 16 of the cap 15 can bealigned with the horizontal indicator line 17 a of the housing. Eachhorizontal marking 16 on the cap 15 represents a reduction or increasein potential fluid needle movement of 0.1 mm. In this way, the spray gunis provided with an accurate, repeatable adjustment of the fluid needle43 in a similar manner to that of a micrometer.

If cleaning of the fluid needle 43 is required, the cap 15 can simply beunscrewed from the gun housing and detached along with the fluid needle43.

The embodiment shown in FIGS. 1 and 2 is of a manual spray gun in whichthe spray material is fed in under pressure via a fluid inlet 50. Afluid passage 51 then conveys the spray material through the handleportion 19 of the gun to the fluid tube 44.

The embodiment shown in FIG. 3 is also a manual spray gun 100 and itoperates in the same manner as the embodiment of FIGS. 1 and 2. Thus,the same reference signs are used for the shared components and will notbe described further here. However, where this second embodiment 100differs from the first embodiment is that the fluid is fed into the gunfrom a reservoir under gravity. Thus, fluid inlet 60 is located on thetop of the gun 100 in this embodiment, and the fluid reservoir (notshown) may be simply screwed into the inlet 60. The fluid is then passeddirectly into the fluid tube 44 of the gun for delivery to the fluid tip45 and nozzle 30.

FIG. 5 shows a longitudinal cross-section through a third embodiment 150of the spray apparatus, which is a further modification of the firstembodiment of the apparatus shown in FIGS. 1 and 2. As with the secondembodiment 100, the third embodiment of the gun 150 has many of thefeatures of the first embodiment 10. Those shared features have the samereference numerals in FIG. 5 and will not be described further. However,where the third embodiment 150 differs from both the first and secondembodiments 10,100 is that the gun uses pneumatic rather than mechanicaloperation of the needle valve. As a result, the third embodiment 150does not have a sliding fluid control sleeve on the housing. Instead,the inlet to the chamber 26 is provided with a bore 32 which directs aportion of the pressurised gas in the passageway 21 to act directly uponthe piston 42. The needle 43 is adapted with a flange 33 which islocated between the needle spring 46 and the piston 42. Thus, as thepressurised gas in the bore 32 acts upon the piston 42, the piston 42 inturn acts upon the needle flange 33, moving the needle 43 away from theseat of the fluid tip 45.As gas is now acting upon the piston 42directly, O0-ring seals are added to the piston 42 itself and at thebase of the end cap 15 so that there is no loss of pressurised gasduring operation.

The purpose of the third embodiment 150 of the gun is to provide amanual spray gun where the fluid needle is operated without the need fora mechanical action. Once the trigger 18 is pulled and the piston bore25 aligns with the passageway 21 to allow gas into the chamber 26, gaswill enter the bore 32 and act upon the piston 42. However, the end cap15 operates as previously described to limit the movement of the needle43 and hence control the amount of fluid released at the nozzle 30. Oncethe trigger 18 is released, a trigger return spring 34 returns thetrigger 18 and thus closes the passageway 21. With the gas to the piston42 cut off, the piston 42 and needle 43 return to the closed positionunder the action of the return spring 46.

FIGS. 5(a) and 5(b) show plan and side elevation views, respectively, ofa fourth embodiment of the present invention. The fourth embodimentdiffers from the previously described embodiments in that it is anautomatic spray gun rather than a manual gun. The automatic gun,generally designated 200, shares a number of components with theprevious embodiments. The gun comprises a housing 211 upon which an aircap 213 is held by an air cap ring 213 a which is threadedly received onthe housing 211. In addition, a regulating valve 214 is provided forcontrolling the spray pattern of the gun 200, and a needle valve cap 215is also provided in order to limit the longitudinal adjustment of thefluid needle of a needle valve, as described in respect of the first andsecond embodiments.

Turning now to FIGS. 6 and 7, the operation of the automatic gun 200will be described in more detail. Generally, the atomising gas passesthrough the gun in the same manner as with the previous embodiments,except that the gas in this instance is supplied by a remote operatedvalve (not shown), rather than a trigger-operated valve. The gas entersthe gun 200 at atomising gas inlet 220 and enters output chamber 226.

The chamber 226 has a radius of curvature 229 at its inlet end so thatthe incoming atomising gas is directed in a horizontal direction throughthe output chamber 226 towards the output nozzle 230. Furthermore, theportion of the chamber 226 adjacent the nozzle 230 has an inner surface231 which has a radius of curvature which allows the inner surface 231to taper inwardly to the point where it reaches the output nozzle 230.

Partially located within the output chamber 226 is a control needlevalve, generally designated 240. The control needle valve 240 comprisesa fluid tube 244 and a fluid tip 245, where a fluid needle 243 extendsforward through the fluid tube 244 to rest in a seat of the fluid tip245. A needle spring 246 biases the fluid needle 243 such that it sitsin the seat at the fluid tip 245, thereby blocking the exit of fluidfrom the fluid tube 244 to the output nozzle 230. The diameter of thefluid tip 245 is sized so as to be no greater than the diameter of thefluid tube 244, to prevent disruption to the gas flow through the outputchamber 226 to the nozzle 230. This embodiment again shows the use of afluid tube 244 which has a narrower throat portion 244 a within theoutput chamber 226. The throat portion 244 a can be provided so as toprovide a smoother passage for the gas as it leaves the gas inlet 220and enters the chamber 226.

As this embodiment of the invention is an automatic gun, the trigger,control sleeve, needle housing and return spring piston necessary in themanual gun are replaced by an operating piston 250 which is housedwithin a piston housing 252 threadedly attached to the main housing 211of the gun. The cap 215 operates in the same manner as described abovefor the previous embodiments so as to restrict the movement of the fluidneedle 243 to regulate fluid flow. The markings and indicator linesdescribed in respect of the first and second embodiments may also beused in respect of the automatic gun so that the micrometer-styleadjustment of the spray may be achieved. The only difference is that theindicator lines are provided on a lock nut 251 which prevents accidentaladjustment of the cap 215. As with the previous embodiments, the fluidneedle 243 may be withdrawn from the gun completely for cleaning, as thecap 215 has an internal flange (not shown) which picks up the end of theneedle 243 adjacent the cap 215.

The piston 250 is operated by pressurised gas entering the pistonhousing 252 from a piston gas inlet 253. As with the atomising gas, thepiston gas in controlled by a valve means remote from the gun itself. Asthe piston gas enters the piston housing 252, the gas pushes the piston250 back and into contact with a flange 254 on the needle 243.Therefore, as the piston 250 moves back, the needle 243 also moves back,thus opening the fluid tip 245 to spray material located in the fluidtube 244 which has entered the fluid tube 244 via a fluid inlet 260. Anabutment (not shown) on the inside of the cap 215 then comes intocontact with the needle 243, thus restricting movement of the needle243. Therefore, if the cap 215 is screwed clockwise onto the housing itwill lessen the amount of movement possible by the needle, and if it isscrewed anti-clockwise it will increase the amount of needle movement.Hence, fluid flow in the gun is controlled by the adjustment of the cap215.

FIG. 7 shows a cross-section of the embodiment of FIGS. 5 and 6, butalong section line VII-VII. The main purpose of this cross-section is toillustrate the lateral taper of the output chamber 226, which can beincluded in any of the previously described embodiments. As can be seenin FIG. 7, the inner surface 270 of the chamber 226 tapers laterallyoutwardly from inlet to outlet. This taper again aids the smooth flow ofgas through the gun.

FIGS. 8(a) and (b) show a fifth embodiment of the spray apparatus, whichis an adaptation of the fourth embodiment of the apparatus. The fifthembodiment shares the majority of the features of the fourth embodimentand these will not be described further here, but are shown with thesame reference numerals in FIGS. 8(a) and (b). Where the fifth andfourth embodiments differ is that the end cap 215 in the fifthembodiment has been adapted so as to provide fine adjustment of themovement of the needle valve 243. The only differences visible fromoutside the apparatus, as shown in FIG. 8(a), are that the end cap 215now fits over the end of the piston housing 252 and is provided withcalibrations 216. The calibrations 216 are viewed against a referenceline 217 on the piston housing 252.

FIG. 8(b) shows the adaptations to the end cap 215 in more detail. Itcan be seen that the end cap 215 has internal threads 270 whichco-operate with external threads 272 on the outside of the pistonhousing 252. With the calibrations 216 on the end cap 215, the operatorcan easily adjust the permitted movement of the needle 243 to obtain aprevious setting. Thus, there is no longer a need for the lock nut ofthe previous embodiment. Otherwise, the fifth embodiment operates in thesame way as the fourth embodiment.

An advantage of the present invention over existing spray apparatus isthat pressure loss across the gun from gas inlet to the nozzle isreduced thanks to the efficient flow of gas through the gun. In themanual embodiment, the gas passageway is substantially straight and thecontrol valve bore is the same size as that of the passageway so thatthe flow of gas is uninhibited when the control valve is open. In boththe manual and automatic embodiments the inlet to the output chamber hasan increased diameter to allow a gradual curve of the gas flow into asubstantially horizontal direction through the chamber. Furthermore,with the lateral taper of the chamber wall and the inward taper adjacentthe output nozzle, gas flow through the chamber is smooth. The gas flowis further aided as the diameter of the fluid tip of the needle valvedoes not protrude outwith the diameter of the fluid tube and the fluidtube has a tapered throat section in the output chamber.

A further advantage of the present invention is that by providing thecap markings and indicator lines on the gun housing, the operator of thegun may adjust the spray of the gun to an exact setting previously used.This repeatability means that there no longer a need for the operator towaste valuable time experimenting to retrieve a previously used sprayratio.

A possible modification to the present invention would be to incorporatea radioactive ionising source such as a radioactive ionising cartridge,for example, into the atomising gas inlet. Introducing such a sourcewould ionise the atomising gas and would overcome problems associatedwith static charge build up on atomised spray droplets.

This and other modifications and improvements can be incorporatedwithout departing from the scope of the invention.

1. An apparatus for spraying liquid surface treatment material, theapparatus comprising: a liquid inlet for supply of the liquid surfacetreatment material; a gas inlet for supply of pressurized gas to bemixed with the liquid surface treatment material; an outlet nozzlethrough which the gas and liquid surface treatment is sprayed; a controlneedle valve arranged for axial movement on a first axis and adapted toregulate the supply of the liquid surface treatment material to theoutlet nozzle; a gas valve operable between an open position and aclosed position; a gas chamber communicating with said outlet nozzle andarranged to co-axially surround the control needle valve; and a gassupply passageway having first and second portions with first and seconddiameters, respectively, the first portion connecting said gas inlet andsaid gas valve and the second portion connecting said gas valve and saidgas chamber; wherein the first and second portions of the gas supplypassageway are coaxial and the first and second diameters aresubstantially equal such that the gas supply passageway hassubstantially the same diameter over its entire length.
 2. The apparatusof claim 1, wherein said gas chamber has a first end portion adjacentthe gas supply passageway, the first end portion having a radius ofcurvature so as to provide gas to the nozzle in a directionsubstantially parallel to said first axis, and wherein said apparatus isadapted to provide a smooth flow path for the gas therethrough.
 3. Theapparatus of claim 2, wherein said radius of curvature is such that theminimum radius of the internal surface of the first end portion of thegas chamber is 1.3 times the diameter of the gas supply passageway. 4.The apparatus of claim 2, wherein the gas chamber has an inner surfacewhich tapers laterally outwardly from the first end portion of the gaschamber, the taper running in the direction of said outlet nozzle. 5.The apparatus of claim 2, wherein said gas chamber includes a second endportion adjacent said outlet nozzle, the inner surface of said secondend portion inwardly tapering towards said nozzle to provide a smoothflow path for gas flowing from the outlet chamber to the nozzle.
 6. Theapparatus of claim 1, wherein said gas valve is located within said gassupply passageway.
 7. The apparatus of claim 1, wherein said gas valveis an axially-sliding piston valve having an aperture therein whosediameter is substantially equal to the diameter of the gas supplypassageway.
 8. The apparatus of claim 1, wherein said apparatus furthercomprises a trigger means adapted to operate both said control valve andsaid gas valve.
 9. The apparatus of claim 1, wherein said control needlevalve is partially located within said gas chamber and includes a fluidtube having a fluid tube diameter and a fluid tip having a fluid tipdiameter substantially equal to or less than the fluid tube diameter.10. The apparatus of claim 9, wherein said fluid tube has a taperedthroat portion located in said gas chamber, the throat portion having athroat portion diameter which is less than the fluid tube diameter. 11.An apparatus for spraying liquid surface treatment material, theapparatus comprising: a housing; a liquid inlet for supply of the liquidsurface treatment material; a gas inlet for supply of pressurized gas tobe mixed with the liquid surface treatment material; an outlet nozzlethrough which the gas and liquid surface treatment is sprayed; a controlneedle valve adapted to regulate the supply of the liquid surfacetreatment material to the outlet nozzle; a gas supply passagewayconnecting said gas inlet to said outlet nozzle; and a control means forcontrolling the control needle valve, the control means comprising a capmember received on said housing and engaged with said control needlevalve, the cap member being adapted so as to be adjustable in the axialdirection relative to the housing to limit axial movement of the controlneedle valve.
 12. The apparatus of claim 11, wherein said cap member andhousing are provided with calibrations which indicate the amount ofaxial adjustment of the needle valve.
 13. The apparatus of claim 11,further comprising a gas valve operable between an open position and aclosed position.
 14. The apparatus of claim 13, wherein the gas valve islocated in the gas supply passageway.
 15. The apparatus of claim 13,further comprising a trigger means adapted to operate both said controlneedle valve and gas valve.
 16. The apparatus of claim 13, wherein saidcontrol needle valve and gas valve are remotely operated.
 17. Theapparatus of claim 16, wherein the control needle valve is remotelyoperated by way of pressurised gas.
 18. The apparatus of claim 17,further comprising a piston chamber and a piston located in the pistonchamber, the piston adapted to engage said needle control valve whenactuated by said pressurised gas.
 19. The apparatus of claim 18, furthercomprising a bore connecting the gas supply passageway and the pistonchamber, such that pressurised gas may pass through the bore to thepiston chamber when the gas valve is in the open position.